Grain Friction Controls Characteristics of Seismic Cycle in Faults With Granular Gouge

Abstract

Mature faults at their core contain granular gouge, created due to communition of host rocks, which its frictional behavior controls earthquake nucleation and rupture patterns. In this work, we consider a fault system with granular gouge to study the effect of grain friction on the characteristics of seismic cycles. Our results show that particle friction controls the evolution of fault frictional strength as well as accumulation and release of elastic strain energy. Our discrete element simulations show that the stick-slip frictional strength and dilation of the fault, as well as their variations, nonlinearly increase with the particle friction, but at high particle friction saturate. By statistical analyses on a large number of slip events, we find that the average recurrence time and its variations decrease with particle friction. A fault with higher grain friction shows more small slip events and also contains a limited number of extreme events. High particle friction introduces a more complex nucleation phase with higher stored energy and many recurrent small failures. We analyze the pseudo acoustic emission, which is based on monitoring the velocity signal of particles, and find higher temporal and more spatially distributed pseudo acoustic emissions for fault with higher grain friction. Our findings in this study show that, in faults with granular gouge, where the fault zone walls are totally engaged to the gouge layer, the friction at grain-scale controls the characteristics of stick-slip cycles including timing and amount of energy release.